In a field of cell medical treatment, when cells that are used in therapy are administered to a patient, the cells are administered to the patient immediately after the cells are sampled from a living body in some cases and are administered to the patient again after the cells are once cultured in vitro in other cases. The cells that are used in therapy are washed with a suspension appropriate for the therapy, are subjected to a cell preparation process such as concentration into a volume appropriate for administration, and then, are transplanted in general. The washing indicates replacement of body fluid, a culture medium, or the like in which the cells are suspended by physiological saline, infusion, or the like. Unnecessary impurities in a cell concentrate can be removed by performing washing treatment in which dilution and concentration are repeatedly performed on the cell concentrate, thereby preferably using the cell concentrate for transplantation into human and animals.
The cells that are used for the cell medical treatment are valuable and the cells capable of being obtained are limited in many cases. Therefore, loss of the cells in the cell preparation process should be minimized. Further, components mixed in the suspension need to be removed by washing as much as possible because the components possibly give an adverse effect on the therapy.
In view of the above-mentioned circumstances, preparation of the cells with reduced loss of the cells while mixing of unnecessary components in the cell suspension is minimized in the cell preparation process is an important object, which can influence treatment results thereafter.
As a cell preparation method, for example, concentration and washing operations using centrifugation have been known. In a method using the centrifugation, the cell suspension is stored in a sealed container and is made to settle by centrifugation for concentrating and washing the cells. Thereafter, the container is opened by a clean bench or the like and supernatant in the suspension is removed. In this case, there is a concern over a possibility that the cells are released to the atmosphere and quality thereof is deteriorated due to contamination or the like. Although a centrifugal operation in a closed system has been proposed (Patent Document 1) in order to cope with the concern, increases in device size and cost are concerned.
Further, as another cell preparation method, a method of concentrating and washing a cell suspension using a rotary membrane filter has been proposed (Patent Document 2). This method can reduce a device in size and simplify the device and enables cells to be handled aseptically in a circuit of a closed system. However, the above-mentioned Patent Document 2 discloses that in order to automatically perform concentration and washing steps, a weight of a storage container is measured by a weight scale and change in weight is fed back to step control so as to automatically perform the steps. However, with the control based on the change in weight, there are concerns over accuracy and responsiveness, a concern over accurate switching of the steps, and a concern over quality deficiency because concentration and washing of the cell suspension are not performed accurately.
In order to cope with the concerns, a filtrating and washing system using a filtrating unit has been proposed (Patent Document 3). The system is a system in order to reuse patient blood lost in a surgery or the like. Patent Document 3 discloses that a blood volume stored in a storage tank is kept within a constant range using a level sensor detecting a liquid level of blood stored in the storage tank in this system. In this method, air bubbles in the system are detected by an air bubble detector and the steps are controlled. Control is made based on the detection of the air bubbles in this manner, thereby rapidly grasping the liquid volume in the circuit accurately. With this, switching of the steps can be expected to be performed immediately and accurately. Meanwhile, the system is used for blood as a target and mixing of the air bubbles in blood treatment is harmful. Therefore, the system detecting air bubbles is not supposed to be applied to a concentration system for removing the unnecessary components and reducing the volume to be administered as objects in the cell preparation process. Further, in the concentration system targeted on the blood, hollow fibers are used as in the above-mentioned Patent Document. Alternatively, when a hollow fiber membrane is used, there are concerns over an adverse effect by mixing of the air bubbles on separation performance of the hollow fibers and washing efficiency depending on types of the hollow fibers.